Method and apparatus for coating a continuous sheet of material



APril 1963 R. v. D. STRONG 3,086,889

METHOD AND APPARATUS FOR COATING A CONTINUOUS SHEET 0F MATERIAL FiledMarch 21, 1960 INVENTOR. RICHARD V. D. STRONG ATTORNEY 3,086,889 METHODAND APRARATUS FQR COATHQG A CONTINUOUS SHEET F MATERIAL Richard V. D.Strong, Meadowbrook, Pa, assignor to F. J. Stokes Corporation,Philadelphia, Pa, a corporation of Pennsylvania Filed Mar. 21, 1960,Ser. No. 164% 8 Claims. (Cl. 117--227) The present invention relates toa method and apparatus for coating a continuous sheet of material, andmore particularly to a method and apparatus for applying a thincontinuous metal film or a uniform thickness to a dielectric sheetmaterial in a continuous operation.

The coating method herein concerned is one in which the sheet materialto be coated is passed continuously through a 'low pressure chamber orzone in which a coating metal is vaporized. The vaporized metal depositson the material to form the coating. In such a process a major problemhas been to obtain a coating which is of uniform thickness along theentire length of the sheet material. For many purposes, as in theproduction of metal coated paper or electrical condensers, variations ofcoating thicknesses cannot be tolerated.

It is an object of the present invention to provide a novel coatingapparatus.

It is another object of the present invention to provide a novelapparatus for coating a continuously moving sheet material with a thinmetal tilm.

It is still another object of the present invention to provide anapparatus for applying a thin metal film of a uniform thickness to acontinuously moving sheet material.

It is a further object of the present invention to provide a method forthe application of a thin continuous metal film of a uniform thicknessto a continuously moving sheet material.

Other objects will appear hereinafter.

For the purpose of illustrating the invention there is shown in thedrawings a form which is presently preferred; it being understood,however, that this invention is not limited to the precise arrangementsand instrumentalities shown.

The drawing is a schematic sectional view of the coating apparatus ofthe present invention.

Referring to the drawing, the coating apparatus of the present inventionis generally designated as 10.

Coating apparatus 10 comprises a housing 12 which is completely enclosedso that the interior of the housing is hermetically sealed from theatmosphere. The housing 12 contains an evaporation chamber 14 along thebottom portion thereof, and a coating chamber 16 above the evaporationchamber 14. A horizontal partition 18 divides the evaporation chamber 14from the coating chamber 16. The partition 18 has an opening 20therethrough adjacent one side of the housing 12 to permit the coatingmetal vapors to pass from the evaporation chamber 14 to the coatingchamber 16. The partition 18 also has an opening 22 therethrough topermit equalization of the pressures within the coating chamber 16 andthe evaporation chamber 14. A pipe 24 connects the interior of theevaporation chamber 14 to means for creating a vacuum, such as a vacuumpump, not shown.

A container 26 of a thermal insulation material is mounted within theevaporation chamber '14 directly beneath the opening 20 in the partition18. The container 26 contains a heater 28, such as an electricalresistance heater. A boat or cup 30 of a material which will withstandhigh temperatures is seated in the container 26 above the heater 28. Theouter wall 62 of the boat 30 tapers so that the area encompassed by thebottom portion of the wall 32 is smaller than the area encompassed bythe top portion of the wall 32. The boat 30 contains the 3,086,889Patented Apr. 23, 1963 source of the coating metal 34. A reel 36containing a strip or wire 38 of the coating metal is rotatably mountedon the side wall of the housing 12 within the evaporation chamber 14.The strip or wire 38 of the coating metal passes from the reel 36between a pair of mating teed rolls 40 and 42, and through a guide tube44 to the boat 30. The feed roll 49 is driven by an electric motor 46mounted outside of the housing 12. The frictional engagement between therotating feed roll 40 and the strip or wire 38 feeds the strip or wire38 to the boat 30 so as .to maintain a constant supply of the coatingmaterial 34 within the coat 30.

A supply roll 48 of the sheet material 50 to be coated is rotatablymounted about a horizontal axis within the coating chamber 16 adjacentthe top of the housing 12. A backing plate 52 is mounted slightly abovethe partition 18, and extends across the opening 29 in the partition 18.A pair of guide rolls 54 and 56 are rotatably mounted along each side ofthe backing plate 52. The sheet material 50 to be coated passes from thesupply roll 48 downwardly to and around the .guide roll 54. The sheetmaterial 50 then passes under the backing plate 52 and across theopening 20 in the partition 18. From the guide roll 56, the sheetmaterial 50 passes upwardly around a pair of vertically spaced guiderolls 58 and 60 to a take-up roll 62 which is mounted adjacent thesupply roll 48.

The take-up roll 62 is driven by an electric motor 64 which is mountedon the top of the housing 12. Motor 64 is electrically connected to asource of electrical current through a speed control 66. A tachometer 68is mounted on the side of the housing 12, and is connected to the guideroll 60. The tachometer 68 continuously measures the speed of rotationof the guide roll 60 as the sheet of material 50 passes around the guideroll 60. The tachometer 68 is electrically connected to the speedcontrol 66 of the motor 64. Any variations in the speed of rotation ofthe guide roll 60 from a predetermined setting of the tachometer 68 willoperate the speed control 66 to vary the speed of the motor 64. Thespeed of the motor 64 is varied to change the speed of rotation of thetake-up roll 62 so that the speed of rotation of guide roll 60 isreturned to the predetermined speed through the variation in the speedof the sheet of material 50. Thus, as the linear speed of the movementof the sheet matrial 50 increases as more of the material 50 is wound onthe take-up roll 62, the tachometer 68 will operate the speed control 66to slow down the motor 64 and thereby maintain the linear speed of thesheet material 50 constant.

A pair of electrical contacts 70 and 72 engage the coated side of thesheet material 58 at spaced points between the guide rolls 58 and 60.The contacts 70 and 72 are mounted on the ends of posts 74 and 76 whichextend through and are supported on the side of the housing 12. Theposts 74 and 76 are insulated from the housing 12 by bushings 78 of anelectrical insulating material. The posts 74 and 76 are electricallyconnected by wires 80 and 82 respectively to a resistance measuring andcontrol circuit, generally designated as 84, The resistance measuringand control circuit 84 may include a bridge circuit which is balancedagainst the resistance measured between the contacts 70 and 72. Such abridge circuit is of the type which will provide an electrical signalupon any variation in the resistance measured between the contacts 70and 72, which signal is of a polarity determined by whether theresistance measured between the contacts 70 and 72 increases ordecreases. There are many types of resistance measuring bridges wellknown in the which will function in this manner, such as the resistancemeasuring bridge shown and described in Patent No. 2,545,576 to PhilipGodley, 2nd issued March 20, 1951.

The resistance measuring and control circuit 84 may also include arheostat which is operated by the signal from the bridge circuit in themanner shown in Patent No. 2,545,576. The rheostat is electricallyconnected by the wires 86 and 88 to the motor 46 which drives the feedroll 48 for the strip or wire 38. The resistance measuring and controlcircuit 84- is connected to the motor 46 so that an increase in theresistance measured between the contacts 70 and 72 will increase thespeed of the motor 46, and a decrease in the resistance measured betweenthe contacts 70 and 72 will decrease the speed of the motor 46.

The coating apparatus 18 of the present invention operates as follows:

The evaporating chamber 14 is evacuated through the pipe 2d which isattached to a vacuum pump. Evacuation of the evaporating chamber 14 alsoevacuates the coating chamber '16 which is in communication with theevaporating chamber 14- through the opening 22 in the partition 18. Themotor 64 is turned on to rotate the take-up roll 62 and thereby pull thesheet material 50 to be coated from the supply roll 48, and across theopening 28 in the partition 18 and across the contacts 70 and 72. Aspreviously described, the tachometer 68 controls the speed of the motor62 through the speed control 66 to maintain a constant linear speed ofthe sheet material 50.

The heater 28 within the container 26 is turned on to heat the coatingmaterial 34 to the temperature at which the coating metal 34 willevaporate at the pressure within the evaporation chamber 1-4. The vaporsfrom the coating metal 34!- ditfuse upwardly through the opening 20 inthe partition 18, and condense on the surface of the sheet material 50to provide a film of the metal on the sheet material 50. Thus, as thesheet material 50 is pulled across the opening 20 in the partition 18,the surface of the sheet material 58 is coated with a film of the metal34, which film is of a thickness according to the amount of the vaporswhich contact and condense on the sheet material 50. The strip or wire38 of the coating metal is constantly fed from the supply reel 36 by thefeed roll 40 into the boat 30 to maintain a desired amount of thecoating metal 34 within the boat 30. The amount of the coating metal 34within the boat 30 determines the amount of the vapors which evaporatefrom the coating metal 34, and thereby determines the thickness of themetal film coated on the sheet material 50. Since the outer wall 32 ofthe boat 30 tapers, the more coating metal 34 within the boat 38 thegreater the surface area of the coating metal 34, and the greater theamount of vapors which will evaporate from the coating metal 34.

As the coated sheet material 50 passes across the contacts 70 and 72,the resistance value of the portion of the metal film between thecontacts 70 and 72 is constantly measured by the resistance measuringand control circuit 84. It is well known that the electrical resistanceof a thin metal film varies with the thickness of the film, with theelectrical resistance decreasing with an increase in the thickness ofthe metal film. The resistance measuring and control circuit 84 isbalanced against a resistance value which is provided by a metal film ofthe desired thickness. Thus, as long as the metal film coated on thesheet material 50 is of the desired thickness, the resistance measuringand control circuit 84 will remain balanced.

However, if the thickness of the metal film coated on the sheet materialincreases, the resistance measured between the contacts '70 and 72 willdecrease causing an unbalance of the resistance measuring and controlcircuit 84. The unbalance of the resistance measuring and controlcircuit 84- caused by a decrease in the resistance be tween the contacts78 and 72 will operate the rheostat of the control circuit 84 todecrease the speed of the motor 46. This in turn decreases the amount ofthe strip or wire 38 of the coating metal being fed into the boat 30 soas to decrease the amount of the metal 34 within the boat 30. Thus, theamount of vapors evaporated from the metal 34 is decreased to decreasethe thickness of the 4 metal film coated on the sheet material 50 untilthe thickness of the metal film applied to the sheet material 50- isback to a desired thickness.

If the thickness of the metal film coated on the sheet materialdecreases, the resistance across the contacts 70 and 72 increases. Theincrease in the resistance value across the contacts '70 and 72unbalances the resistance measuring circuit 84 so that the rheostat ofthe circuit 84 increases the speed of the motor 46. This in turnincreases the speed of the feed of the strip or wire 38 into the boat 38so as to increase the amount of the metal 34 within the boat 38. Thus,the amount of vapors evaporated from the metal 34 is increased toincrease the thickness of the film coated on the sheet material 50 backto the desired thickness.

Thus, in the coating apparatus 10 of the present invention, the sheetmaterial 50 is moved at a constant speed across the opening 20 where thesurface of the sheet material 50 is coated with a thin film of metal.Any variations in the thickness of the film of metal coated on the sheetmaterial 50 causes the resistance measuring and control circuit 84 toproperly operate the motor 46 so as to vary the amount of coatingmaterial in the boat 30. The variations in the amount of the metalwithin the boat 30 varies the amount of vapors evaporated from thecoating metal within the boat 30 in a manner to compensate for anyvariations in the thickness of the metal film on the sheet material 50.Thus, variations in the thickness of the metal film are automaticallycompensated for to provide the sheet material 50 with a coating of themetal which is of substantially uniform thickness.

The present invention may be provided with specific forms Withoutdeparting from the spirit or essential attributes thereof and,accordingly, reference should be made to the appended claims, ratherthan to the foregoing specification as indicating the scope of theinvention.

I claim:

1. Apparatus for coating a continuously moving sheet of material with ametal film comprising a housing, means for evacuating said housing, aboat Within said housing for containing the coating metal, means forheating said boat to evaporate the coating metal, means for continuouslymoving the sheet of material across the boat to continuously expose thesheet of material to the metal vapors difiusing from the boat, means forcontinuously measuring the electrical resistance per unit length of themetal film coating on the sheet of material, the improvement comprisingmeans operated by a variation in the resistance measured to vary thesurface area of the coating metal within the boat.

2. Apparatus for coating a continuous moving sheet of material with ametal film comprising a housing, means for evacuating said housing, aboat within said housing for containing the coating metal, means forheating the boat to evaporate the coating metal, a supply reel of astrip of the coating metal within said housing, means for feeding saidstrip to said boat, means for continuously moving the sheet of materialacross the boat to expose the sheet of material to the metalvaporsdifiusing from the boat, means for continuously measuring the electricalresistance per unit length of the metal film coating on the sheetmaterial, the improvement comprising means operated by a variation inthe resistance measured to vary the speed of the feed of the strip intothe boat to vary the surface area of the coating metal in said boat.

3. Apparatus in accordance with claim 2 in which the means for varyingthe speed of the feed of the strip increases the speed upon an increaseof the resistance measured, and decreases the speed upon a decrease ofthe resistance measured.

4. Apparatus in accordance with claim 2 in which the boat has an outerwall which tapers outwardly from the bottom of the boat.

5. Apparatus for coating a continuously moving sheet of material with ametal film comprising a housing having an evaporating chamber and acoating chamber sepa rated by a common partition, said pantition havingan opening therethrough, means for evacuating said housing, a boatwithin said evaporating chamber beneath the opening in the partition,means for heating said boat, a supply reel of the strip of the coatingmetal mounted in said evaporating chamber, means for feeding said stripof coating metal into said boat, a supply roll of the sheet of materialrotatably mounted within the coating chamber, a take-up roll mountedWithin said coating chamber, means for guiding said sheet of materialfrom said supply roll to said take-up roll so that the sheet of materialpasses across the opening in the partition, means for rotating saidtake-up roll, a pair of contacts mounted in spaced relation along thepath of travel of the sheet of material between the opening in thepartition and the take-up roll, said contacts being adapted to engagethe metal coating on the sheet of material, means for measuring theelectrical resistance between said contacts, the improvement comprisingmeans operating by a change in the resistance between said contacts tochange the speed of the feed of the strip of coating material into theboat to vary the surface area or the coating metal in said boat.

6. Apparatus in accordance with claim 5 in which the means for varyingthe speed of the feed of the strip increases the speed upon an increaseof the measured resistance and decreases the speed upon a decrease ofthe measured resistance.

7. Apparatus in accordance with claim 6 in which the boat has an outerwall which tapers outwardly from the bottom of the boat.

8. A method of coating a continuous sheet of material with a metal filmcomprising feeding a coating metal into a boat, heating said boat tovaporize the coating metal, continuously moving the sheet of materialacross the top of the boat, continuously exposing the sheet of materialto the metal vapors from the boat, continuously measuring the electricalresistance per unit length of metal film applied to the sheet ofmaterial, and varying the amount of material fed into the boat to varythe surface area of the coating metal in said boat according tovariations in the measured resistance.

References Cited in the file of this patent UNITED STATES PATENTS2,273,941 Dorn Feb. 24, 1942 2,545,576 Godley Mar. 20, 1951 2,750,921Purdy June 19, 1956 2,772,318 Holland Nov. 27, 1956 2,366,065 Hirsh Dec.23, 1958 2,978,364 Blaustein Apr. 4, 1961 FOREIGN PATENTS 288,438Switzerland May 16, 1953 752,141 Germany Feb. 1, 1954

8. A METHOD OF COATING A CONTINUOUS SHEET OF MATERIAL WITH A METAL FILMCOMPRISING FEEDING A COATING METAL INTO A BOAT, HEATING SAID BOAT TOVAPORIZE THE COATING METAL, CONTINUOUSLY MOVING THE SHEET OF MATERIALACROSS THE TOP OF THE BOAT, CONTINUOUSLY EXPOSING THE SHEET OF MATERIALTO THE METAL VAPORS FROM THE BOAT, CONTINUOUSLY MEASUREING THEELECTRICAL RESISTANCE PER UNIT LENGTH OF METAL FILM APPLIED TO THE SHEETOF MATERIAL, AND VARYING THE AMOUNT OF MATERIAL FED INTO THE BOAT TOVARY THE SURFACE AREA OF THE COATING METAL IN SAID ACCORDING TOVARIATIONS IN THE MEASURED RESISTANCE.